Role of Surface Roughness in Tribology:From Atomic to Macroscopic ScaleVorgelegt vonMast.-Ing.Chunyan Yangaus Hebei, ChinaVon der Fakult¨at V Verkehrs- und Maschinensystemeder Technischen Universit¨at Berlinzur Erlangung des akademischen GradesDoktor der IngenieurwissenschaftenDr.-Inggenehmigte DissertationPromotionsausschlussVorsitzender: Prof. Dr. Ing. Henning Ju¨rgen MeyerGutachter: Prof. Dr. rer. nat. Valentin PopovGutachter: Dr. Bo Nils Johan PerssonTag der wissenschaftlichen Aussprache: 30.06.2008Berlin 2008D 83This thesis was written at the instituteQuantum-Theorie der Materialien, Institut fu¨r Festk¨orperforschung (IFF),Forschungszentrum Ju¨lich GmbH, Ju¨lich, Deutschland.It is available online at the internet pages of the library ofTechniche Universit¨at Berlin.AbstractThe practical importance of friction cannot be underestimated: from the creation of firesby rubbingsticks together, to the current efforts to buildnano devices, friction has playedan important role in the whole history of technology of mankind. Friction is a complexmultiscale phenomenon that depends both on the atomic interactions inside the contacts,onthemacroscopicelasticandplasticbehaviorofthesolidsincontact, andontheunavoid-able, stochastic roughness characterizing real surfaces. Tribology, the science of friction,has developed much in recent years, but many questions are still open.